Even though the brutal murder had all the hallmarks of a gangland hit, John’s minor convictions dated back to the early 1980s and he had no links with organised crime.

But we can reveal he had been living in fear because of a dispute with a major Finglas criminal – and had even bought a gun to protect himself.

Family man...John with a child

Gardai seized the weapon from him last year and a file had been sent to the DPP.

In a tragic double twist we can also reveal:

John’s brother William died in June 2003, two days after two masked gunmen shot him at his home in the New Cabra Road in Finglas

The window cleaner had witnessed two separate murders in Ballymun in 2003 and 2006

He had information about the killing of Michael Scott, who was shot dead on Sillogue Road in April 2003, and

He also witnessed the murder of Gregory Rowan, who was fatally assaulted in Ballymun in August 2006.

Yesterday John became the year’s seventh gun victim after he was blasted at point-blank range just yards from the home he shared with his wife.

He was involved in a long running dispute with local hood in Ballymun.

The feud spilled over a year ago when John was accused of damaging the window of this man’s car.

The man chased him through the streets carrying a chainsaw.

Gardai also looking at the possible involvement of another north Dublin criminal who was himself the victim of a murder attempt in recent months.

A devastated neighbour, who did not want to be named, said: “Thirty years he was my neighbour and he has always been a gentleman.

“He used to even have a key to my flat to keep an eye on things for me when I was away and I know he did a lot to help others so why did he deserve this?

“He cycled round this road every morning to start his window cleaning round and has done for years so who ever shot him knew where to find him.

“It’s only lucky the school kids are on holidays for Easter as the poor things would have saw that horror.

“John even has nieces and nephews at that school so imagine they had witnessed that?”

Detectives last night insisted they have not established a motive for the callous murder.

Another man who came across the daylight bloodbath told the Irish Mirror: “I didn’t see the shooter but I was just coming out of the house when I saw a man lying on the ground.

“He was shaking like he was having a fit and then I could see a bike lying beside him and a bag.

“I did hear five or six bangs but they weren’t very loud and because there’s a lot of building work going on around here I just presumed it was workmen.”

One woman, who used to live beside John’s family in Finglas and moved to Ballymun the same time as him, fought back tears as she insisted he was a “good man”.

She revealed: “I was talking to a woman in the shop who saw it and she’s devastated – she was near sick over it all. No one wants to see that.

“I didn’t know anything about it until I heard sirens and saw a bit of commotion and then I realised it was John who had been shot.

“I was gutted. He used to walk up past my house every day going to the pub or to the bookies and that’s all he did.

“He kept himself to himself and did his windows and that was it. John was a lovely lad.

"He was very quiet and his family are nice too. They’ve had enough heartache in their lives after Willie was shot all those years ago.”

Detectives are trawling through CCTV to try to nail John’s killer and want to identify a cyclist near the scene.

Supt Paul Moan from Ballymun revealed: “What we’re particularly interested in is a person who was leaving Gateway Avenue cycling a bike and who went on to the Ballymun Road.

“What was unusual is he was wearing a high-vis vest and a baseball cap and chose to cycle on the footpaths.

“Because this was around the time of people commuting to work, there were lots of people around at bus stops, many people on buses or travelling in cars and indeed people walking who may have seen this person or accidentally came across him.”

A garda on a motorbike was the first person at the scene and performed CPR until paramedics arrived.

John was still alive when he was taken to the Mater Hospital but died from his injuries shortly before 9.30am.

Fine Gael representative Noel Rock said: “He was a decent fellow. Unfortunately he had witnessed two murders in the past and seems to have been the victim of a targeted killing.

Local election candidate Noel Rock

“It’s as brazen as it gets, and it’s just chance that we’re in the middle of an Easter break and no children were there to witness this horrific scene.

“This isn’t welcome here in Ballymun, and I would condemn it in the strongest possible terms - as would all local people. This is a great community and this kind of criminal activity needs to be ended, whatever the cost.

“People are fed up of this, it’s the seventh gun murder of 2014 already, and more needs to be done to stamp this out. It’s dreadful, and the circumstances have the community very fearful.”

Garda Interim Commissioner Noirin O’Sullivan said the murder would have a “very significant” impact.

She added: “The murder happened in Ballymun which is a very vibrant community on Dublin’s northside. It happened in close proximity, adjacent to a national school.

“Obviously when a murder like this happens, it has a very significant impact on the community.”

Anyone with information is asked to contact Ballymun Garda station on 01 6664400 or the Garda Confidential Telephone Line on 1800 666 111.